Hybrid vehicles may include and engine and an electric machine to propel the vehicle. In some vehicle designs, the engine may have significantly higher output capacity than the electric machine due to packaging and weight constraints. The electric machine may be used to start the engine and to provide a small amount of torque to launch a vehicle in which the engine and electric machine reside. However, the electric machine may not be useful to accelerate beyond vehicle creep speed without assistance from the engine since the electric machine is tasked with accelerating the vehicle and starting the engine. Consequently, the electric machine may provide limited use beyond starting the engine.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method of starting an engine, comprising: during a first condition, starting an engine with a first electrical machine while a driveline disconnect clutch is closed; and during a second condition, starting the engine with a second electrical machine while the driveline disconnect clutch is open.
In other words, the engine may be started by two electric machines during different conditions so that one electric machine may help to provide torque to a vehicle driveline over a broader range of conditions while the other electric machine may have a specific function of starting the engine. For example, a driveline integrated starter/generator may start the engine and provide torque to a driveline during low driver demand torque conditions. Further, the driveline integrated starter/generator may supply torque to the driveline at higher drive demand torque conditions while a lower power output capacity electric machine starts the engine. The lower power capacity electric machine allows the driveline integrated starter/generator to provide driveline torque over a broader driver demand torque range. In this way, a smaller driveline integrated starter/generator may provide a driveline torque function that heretofore required a larger electric machine.
The present description may provide several advantages. Specifically, the approach may extend a driver demand torque range of a driveline integrated starter/generator. Further, the approach may improve engine starting by allowing the engine to accelerate to a speed of the driveline integrated starter/generator before a driveline disconnect clutch is closed.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.